The fast and the flexible: Graphene foam batteries charge quickly

Capacity on par with existing lithium batteries, but charges in 15 minutes.

There are a variety of technologies available for storing energy, each with various tradeoffs in terms of weight, capacity, and performance. For example, capacitors are fast and lightweight but, despite their name, don't have a large capacity. Batteries can hold more charge, but are heavier and take longer to recharge. This diversity is good, in that it provides plenty of options to tailor a device to suit specific needs. But it probably leaves engineers looking longingly at the options they didn't or couldn't choose.

In yesterday's edition of PNAS, however, researchers from China describe a battery design based on graphene foam that may nicely bridge the gap. It's based on existing lithium technology, and even in experimental form, it has a similar capacity:weight ratio. But it can charge and discharge nearly as fast as a capacitor, being able to completely discharge in about 20 seconds. As an added bonus, it's flexible and works fine when you bend it.

Graphene is a single-atom thick sheet of linked carbon atoms, and its remarkable properties made it the winner of the 2010 Nobel Prize in Physics. Chief among those properties are mechanical strength and an ability to conduct electricity with very little resistance.

The focus with graphene has generally been to build larger sheets, but the process for creating graphene foam is quite distinct. To produce it, you first start with a metal foam, which is a three-dimensional mesh of metal filaments. This is used to grow graphene on the metal surface through standard techniques (vapor deposition), after which the metal is processed away. The result is a similar three-dimensional mesh, shown above, but this time constructed of graphene. The foam itself is both flexible and mechanically tough.

The resulting foam has a number of properties that make it a good battery electrode. These include a large surface area (lots of places for charge carriers to exchange electrons) and excellent conductivity (to get those electrons out of the device). It also happens to be very light-weight.

So, the authors prepared an electrode using a lithium-titanium compound (Li4Ti5O12) deposited on the surface of the graphene foam. On its own, LTO with and without graphene foam behaved identically at slow charge/discharge rates. But, as the rate of charging was increased, LTO's performance got dramatically worse, while performance for the LTO/graphene material only declined gradually. Even at a discharge rate that would completely empty the material in 18 seconds, its performance was 80 percent of what it displayed during an hour-long discharge. Plus, performance remained stable through 500 charge/discharge cycles, and the material retained the flexibility of its graphene foam skeleton.

That was good enough for the authors to decide to build a battery: with the LTO material as an anode, a cathode made of LiFePO4/graphene foam, and a standard electrolyte. The battery didn't show quite the excellent charge/discharge performance the individual electrodes had, but it still performed very well at a charge rate that could fill it in under 15 minutes. Even in this lab-based form, which undoubtedly left a number of efficiencies on the table, its energy density was about 110Whrs/kg. That's roughly in line with current lithium batteries.

And the graphene foam worked just fine while by being bent with a radius of curvature of just five millimeters. Repeated flexings only had a small impact on the performance of the battery.

The authors note they haven't optimized the battery production in any way, and expect they could get a much better energy density by implementing any of a number of things. Even in its current state however, there are plenty of potential uses for a battery that's flexible and can charge fully in 15 minutes. The real concern wouldn't seem to be the battery itself though. The production of graphene foam appears likely to be expensive and energy intensive. If the foam can't be made cheap enough, then we're not likely to see this technology commercialized, regardless of how good its performance is.

Why limit it to ebooks? Stick large foam batteries in a vehicle (and provide power stations instead of gas stations with very high power delivery) and you can have an electric car that charges in minutes.

If the efficiency goes up and the cost goes down, we could even reach a utopia where your phone lasts nearly a WHOLE DAY!</sarcasm>

Whenever I read an exciting battery article, I read the last paragraph first:

"The production of graphene foam appears likely to be expensive and energy intensive. If the foam can't be made cheap enough, then we're not likely to see this technology commercialized, regardless of how good its performance is."

Seems to me the problem of weight is the bigger breakthrough than anything else. The Tesla S can reach 80% capacity in under 30 minutes and there are faster, less different solutions already on the way. The biggest issue we really have right now is getting enough power into a device through a little cable safely. You won't get iPhones charged in 10 seconds with the cable they use now.

But the weight, that's huge. Electric cars are all designed around keeping the weight incredibly low to stuff as many heavy batteries in. Keeping the power to weight ratio significantly lower could easily offset the cost, especially in high performance cars (unless we're talking $500k of batteries needed for one car).

Seems to me the problem of weight is the bigger breakthrough than anything else. The Tesla S can reach 80% capacity in under 30 minutes and there are faster, less different solutions already on the way. The biggest issue we really have right now is getting enough power into a device through a little cable safely. You won't get iPhones charged in 10 seconds with the cable they use now.

But the weight, that's huge. Electric cars are all designed around keeping the weight incredibly low to stuff as many heavy batteries in. Keeping the power to weight ratio significantly lower could easily offset the cost, especially in high performance cars (unless we're talking $500k of batteries needed for one car).

I've been keeping an eye on fast-charge Li-ion batteries for certain mobile products that I'm involved in designing. A truly fast charging capability, when coupled with long deep cycle life, are potential "use case" changers in some products that now must hold sufficient energy to last a full shift (plus). Safety is also a factor, particularly in high energy applications. One of the sample batteries that I have in my office is an 11Ah package from Altairnano, which can be charged in under 10 minutes and has a deep cycle life of more than 20K cycles. Note that this is a deep cycle life and for opportunistic charging applications (such as on a factory floor where, as a benefit of fast charging a product could be fully topped up during a coffee break) the cycle life actually goes up. In contrast, the cycle life of conventional Li-ions is pretty short...often under 1K cycles, so Altairnano's 20K+ caught my attention. A123Systems also makes fast charging batteries, and I have some samples of their products, too. However, for many of my applications it's easier to use rectangular form factors.

The game changing factor, I think, is that [safe] fast charging capability can enable opportunistic charging (such as described in the routine of a coffee break mentioned above) and reduce the need for large, high capacity storage devices in some applications. For an example, topping up in 10 to 60 seconds of contact with a charging base might make charging sufficiently convenient to alter how people interact with mobile products. However, the use case must be carefully considered to ensure customers don't have any Black Swan events. Weight, as robrob points out, is also a factor that must be considered in relation to the use case. High energy density, fast charging, and low internal resistance (which plays a role in heating), all seem to entail relatively high weight at the moment, so a low weight alternative, even with poorer energy density, might be very attractive.

For automotive applications, how do you think fast charging would affect commuters? If you could get home on a 10 minute (or less) charge, would that make a shorter range (i.e. lower energy storage capacity) vehicle acceptable?

15 minutes is still probably too long for electric cars to displace gasoline, but it's getting into the territory where I can't rule it out completely. At least for myself.

What if additional development got the charge time down to 12 minutes? Or 10 minutes? Even if recharges never are as fast as filling a gas tank, my gut feeling is that people with complain, but will at some point, just cope with it if they need to.

Why limit it to ebooks? Stick large foam batteries in a vehicle (and provide power stations instead of gas stations with very high power delivery) and you can have an electric car that charges in minutes.

If the efficiency goes up and the cost goes down, we could even reach a utopia where your phone lasts nearly a WHOLE DAY!</sarcasm>

I don't like being at the gas station for more than a couple minutes now for gas, 15+ minutes? Noooo thanks.

Well, the advantage of electricity is that you can install a charge port just about anywhere. Say, the company parking lot or in tandem with a parking meter?

Why limit it to ebooks? Stick large foam batteries in a vehicle (and provide power stations instead of gas stations with very high power delivery) and you can have an electric car that charges in minutes.

If the efficiency goes up and the cost goes down, we could even reach a utopia where your phone lasts nearly a WHOLE DAY!</sarcasm>

Why limit it to ebooks? Stick large foam batteries in a vehicle (and provide power stations instead of gas stations with very high power delivery) and you can have an electric car that charges in minutes.>

I used to picture gas stations as becoming storage facilities for thoroughly standardized battery packs - customers would drive in and simply have their drained packs swapped out for charged ones, pay and off they go!

In the end they'd have an awful lot of packs on hand and yet probably not enough to fulfill their needs, at least at busier "gas" stations or during busy times at many of them - but this situation gets better and better as the technology leads to smaller packs and especially as it takes less and less time to charge a pack (drained packs would obviously automatically be plugged in and charged, ready for next customer in fewer and fewer minutes).

I still think it would be too overwhelming overall - a battery pack does not store quite as easily as 10-20 gallons of gas, and just what kind of power would be needed to charge multiple packs as they come in I don't know. Another issue is maintenance - I think you'd have to have a sort of license deal where you simply get a good battery pack even if yours is somehow bad (like end-of-life) - the costs would be built into the "refill" price in the first place rather than charged on a per-customer basis, hopefully removing the opportunity for hucksters to rip off customers ("Your battery is broken! We're gonna have to charge you an extra $750 for the replacement!").

I like electric cars a lot - I think the Toyota Prius is the most important car we have seen come along in decades on an overall basis (by which I mean counting all factors including most importantly the number sold - lots of people will take exception but they're talking about far more niche models at this point than the Prius), but I'm still lost completely on just how much trouble batteries are in the long run, ecologically speaking.

I've been keeping an eye on fast-charge Li-ion batteries for certain mobile products that I'm involved in designing. A truly fast charging capability, when coupled with long deep cycle life, are potential "use case" changers in some products that now must hold sufficient energy to last a full shift (plus). Safety is also a factor, particularly in high energy applications. One of the sample batteries that I have in my office is an 11Ah package from Altairnano, which can be charged in under 10 minutes and has a deep cycle life of more than 20K cycles. Note that this is a deep cycle life and for opportunistic charging applications (such as on a factory floor where, as a benefit of fast charging a product could be fully topped up during a coffee break) the cycle life actually goes up. In contrast, the cycle life of conventional Li-ions is pretty short...often under 1K cycles, so Altairnano's 20K+ caught my attention. A123Systems also makes fast charging batteries, and I have some samples of their products, too. However, for many of my applications it's easier to use rectangular form factors.

Great analysis, thanks for that.

I'm surprised at all the folks whinging about "too slow for cars". One of the issues people seem to have with electrics is "fear of being stranded", e.g. can I get home? Notice that 15 minutes was to *fill*. In a car with a 150km fully charged range (I pulled that figure out of you-know-where), that gives you 10km per minute of charge. Running low on charge when the wife (or husband) calls to ask for milk? 5 minutes of charging while you're in the store should be more than enough to get you home.

I'd love to see wireless charging pads in grocery store parking lots or whatever. You'll probably pay a significant markup on the raw power costs versus what you'd pay for at home, but I'm guessing that having something like a 0.5 meter^2 pad could allow for high transfer rates with less worry about couplers that can handle that much juice.

Again, if it's easy and convenient to charge, then people generally require *less* range. Routinely driving more than 100-150km in a stretch is *relatively* rare. Even folks in sales who might drive 5,000+km per month (~$4k per year in gas at $4/gallon, 30mpg) will often have routes that have lots of stops, for example.

Again, if it's easy and convenient to charge, then people generally require *less* range. Routinely driving more than 100-150km in a stretch is *relatively* rare. Even folks in sales who might drive 5,000+km per month (~$4k per year in gas at $4/gallon, 30mpg) will often have routes that have lots of stops, for example.

There are still cases where that long distance is necessary. My parents would go to see the grandparents in Chicago from Iowa City. They would drive b/c it's easier and a lot less expensive than buying airline tickets to get there and immediately also renting a car there.

My Mom still goes to visit her sister in Ft. Wayne, IN. She drives there as well. While she has had to gas up on the way, it is only once during the trip there or back.

There are still cases where that long distance is necessary. My parents would go to see the grandparents in Chicago from Iowa City. They would drive b/c it's easier and a lot less expensive than buying airline tickets to get there and immediately also renting a car there.

My Mom still goes to visit her sister in Ft. Wayne, IN. She drives there as well. While she has had to gas up on the way, it is only once during the trip there or back.

I totally agree. The question is how often?

Many households in the US are 2 car households, for example. Would you consider paying $5-10k less for a car that had a 150km range versus, what can a honda civic do? 600km? My guess is that less than 25% of the US non-freight vehicle fleet does a non-stop trip of >150km more than 10 times a year. Which is to say that the vast bulk of miles are relatively short trips. For the relatively rare long trips, use the "long-distance" car. For a big enough price difference, renting a car for 1 week a year for vacation of family trips starts to make sense.

Tangentially, I originally thought the volt's cogeneration capabilities were silly. In retrospect, the idea has really grown on me as an easy way of extending range when long trips are rare.

What i would like to know is where all this electricity is supposed to come from, not necessarily the generation but the delivery. Being able to charge your car's battery in 10-15 min sounds awesome, but as an electrical engineer the amount of energy flowing to the car to do that is pretty staggering. Take the Nissan leaf, it has a 24kw/h battery pack, and Nissan makes a 30 min quick charger that cn get the pack to 80% charge. To do this it dumps 480V @ 125 amps into the batery, that is 60kW of energy, for those that aren't familiar with the scale, if you were to completely max the 200 amp service in your house(if your house even has that large a service) at 220V that's only 44kW.

Think of a Walmart with 6 of these 10min chargers out front, if all three were in use they would be sucking down a full MegaWatt of energy all by themselves. Not to mention the engineering problems presented by the charging leads, unless you drastically increase the voltage of the battery pack, you are going to need to dump 375 amps into the battery to charge it in ten minutes, for that you will need 250kcmil wire at least, probably more like 300kcmil, so you are talking close to an inch in diameter for each conductor and ~60lb of weight for a ten foot lead.

I would love to have truly useful and ubiquitous electric cars, but there is a whole hell of a lot more to solve than just batteries, and it bothers me that I never see anyone talking about these other issues. Maybe it just because until we have the batteries these issues aren't really going to be apparent to most people.

They stack the deck for electrics and people still don't want them. You have to think practically - like the 'range' they suggest is actually 'optimal when new' range and not a real world number. Just as Nissan Leaf owners. They are losing a ton of range even with one year of ownershiip. And hey you want AC or Heat? Well that drains the range too...

So even with cheap electrics unless you live in a place with optimal weather people wont want em.. I dunno about you but the first thing I do with a nice brand new car is go on a road trip.. I don't want a car that I can't drive across the country.

Why limit it to ebooks? Stick large foam batteries in a vehicle (and provide power stations instead of gas stations with very high power delivery) and you can have an electric car that charges in minutes.

If the efficiency goes up and the cost goes down, we could even reach a utopia where your phone lasts nearly a WHOLE DAY!</sarcasm>

EV's are not feasible with the way our economy runs and is governed unfortunately. An ebook reader is a nice safe and easily achievable goal. Also screw cell phones.

Think of a Walmart with 6 of these 10min chargers out front, if all three were in use they would be sucking down a full MegaWatt of energy all by themselves. Not to mention the engineering problems presented by the charging leads, unless you drastically increase the voltage of the battery pack, you are going to need to dump 375 amps into the battery to charge it in ten minutes, for that you will need 250kcmil wire at least, probably more like 300kcmil, so you are talking close to an inch in diameter for each conductor and ~60lb of weight for a ten foot lead.

Thanks, that's a nice wrap-up of the numbers. Two questions:

* Would using a wireless connection over an area reduce issues with leads? How does the power can you reasonably push through a wireless pad scale with its area?* Does the use of short runs of superconducting cable make any sense?

As a thought experiment, how about a charging station that has 20 wireless pads, each with 20 ft superconducting cable running from it's own 50A circuit. Stick a 50MW Toshiba 4S in the center (which can also power your cryodistiller to cool the wires) and you're ready to go. High capital cost, low operating cost, theoretically long lifetime.

Sure, it sounds a little crazy. But when you start factoring in externalities of hydrocarbon fuel delivery to public infrastructure, e.g. cost of fixing road wear from the semi tankers that clock *insane* numbers of road miles per year fully loaded, not to mention the cost of road congestion, asthma, etc., public investment in this type of delivery infrastructure starts to look more attractive once the tech is available.

I think the Toyota Prius is the most important car we have seen come along in decades on an overall basis (by which I mean counting all factors including most importantly the number sold - lots of people will take exception but they're talking about far more niche models at this point than the Prius), but I'm still lost completely on just how much trouble batteries are in the long run, ecologically speaking.

So, simple: each vehicle maintains its own registry of the life of each of its batteries.

When you "fill up", the station charges you appropriately for the capacity/life of each of your cells.

Yes, this opens up a whole new paradigm - how to replace a deforming cell and still maximize vehicle life.

Think of a Walmart with 6 of these 10min chargers out front, if all three were in use they would be sucking down a full MegaWatt of energy all by themselves. Not to mention the engineering problems presented by the charging leads, unless you drastically increase the voltage of the battery pack, you are going to need to dump 375 amps into the battery to charge it in ten minutes, for that you will need 250kcmil wire at least, probably more like 300kcmil, so you are talking close to an inch in diameter for each conductor and ~60lb of weight for a ten foot lead.

Thanks, that's a nice wrap-up of the numbers. Two questions:

* Would using a wireless connection over an area reduce issues with leads? How does the power can you reasonably push through a wireless pad scale with its area?* Does the use of short runs of superconducting cable make any sense?

As a thought experiment, how about a charging station that has 20 wireless pads, each with 20 ft superconducting cable running from it's own 50A circuit. Stick a 50MW Toshiba 4S in the center (which can also power your cryodistiller to cool the wires) and you're ready to go. High capital cost, low operating cost, theoretically long lifetime.

Sure, it sounds a little crazy. But when you start factoring in externalities of hydrocarbon fuel delivery to public infrastructure, e.g. cost of fixing road wear from the semi tankers that clock *insane* numbers of road miles per year fully loaded, not to mention the cost of road congestion, asthma, etc., public investment in this type of delivery infrastructure starts to look more attractive once the tech is available.

While an inductive charging system of this magnitude would certianly be possible it isn't really feasible. An inductive power charger is essentially a air core transformer that isn't physically coupled, these types of transformers lose efficiency very very fast at ranges over practically touching. Getting that kind of power through one would be a technical hurdle but a solvable one if you could get the car's secondary winding close enough to the ground via some sort of drop system. You would likely need to go with a substantially higher voltage to limit current induced losses, but that isn't a big deal since the actual "charger" would need to be in the car since you can't charge a battery with AC current.

Which brings me to the reason it would never be feasible, to charge that leaf's battery in 10 minutes you would need a DC power supply in the range of 150-200kW they make those, they run ~15k$ and are the size of a large refrigerator or larger. Now you would save a good bit of size and weight since you would be using relatively high frequency AC which would reduce the size of the transformers and conditioning circuitry needed but it would still be way too large to practically fit in a car.

As for the superconducting cables, 300kcmil isn't terribly large in the grand scheme of power transmission wire, it would be no big deal to use it to connect the charger to power, it was only listed as a problem because you need to connect the car to the charger as well, and that's a lot of weight to lift to connect the leads, and especially for the connector. Superconducting cables would not be useful in either parts, too expensive and hard to maintain for the the "transmission" lines and not really useable at all for the leads to the car.

To not speak of cars for a change: Even now and even for things like smartphones and tablets it's often not the battery that's limiting how fast you can charge the thing. Using USB for charging puts quite tight limits on the power you can get over the wire, especially when you want to use it to transfer data or attach periphery at the same time.

Or with other words: In many applications there are several bottlenecks to consider. Another one is safety -- go high enough with your voltage and/or current and things start to be dangerous enough to deserve some serious engineering.

Ok here's a crazy idea (I'm a computer scientist so this is a little outside my field): superheat organic material in low-ox to get the carbon structure. It'll probably be low quality, but what if it's still useful?

They write that the energy/kg is similar to existing batteries but the graphene foam's "advantage" is that it is so light. From this I get that it is very bulky for the same stored energy.Although the capacity may refer to the complete battery with standard electrolyte and metals, energy/m^3 may be low.

"The production of graphene foam appears likely to be expensive and energy intensive. If the foam can't be made cheap enough, then we're not likely to see this technology commercialized, regardless of how good its performance is."

Ok here's a crazy idea (I'm a computer scientist so this is a little outside my field): superheat organic material in low-ox to get the carbon structure. It'll probably be low quality, but what if it's still useful?

You don't get graphene that way, you get charcoal, very contaminated as well.

Ok here's a crazy idea (I'm a computer scientist so this is a little outside my field): superheat organic material in low-ox to get the carbon structure. It'll probably be low quality, but what if it's still useful?

Just went to a talk yesterday given by some researchers in my department doing pretty much that. They make an aerogel out of an organic that likes to form chains (I've forgotten the exact chemical but its basically benzene rings linked by oxygens). Once they have the aerogel they freeze dry it before heating it in an inert atmosphere, leaving behind chains of carbon with a stupidly high surface area. Pore size was tunable with heating regime, was typically 5-50 nm, and this affects the density of storage and output, etc.

The problem they have, which I suspect the guys this article is about will be having, is that to recharge they require quite high voltages, which allows the Li ions to react with the carbon electrode. You could reduce this required voltage slightly by messing with pore size, but that also reduced capacity/power density.

So like everything in materials science at the moment its a comprimise between good rechargeability or power density. Tweaking the electrode to inhibit that reaction with Li ions seems to be the logical step.

Think of a Walmart with 6 of these 10min chargers out front, if all three were in use they would be sucking down a full MegaWatt of energy all by themselves. Not to mention the engineering problems presented by the charging leads, unless you drastically increase the voltage of the battery pack, you are going to need to dump 375 amps into the battery to charge it in ten minutes, for that you will need 250kcmil wire at least, probably more like 300kcmil, so you are talking close to an inch in diameter for each conductor and ~60lb of weight for a ten foot lead.

It's always important to consider the details - that's the difference between speculation and engineering. But that doesn't mean there aren't solutions. One possibility for the car-to-charger connection is to get away from the model we all have in mind of a human being sticking a hose in the gas tank. Go with a standardized, powered docking station: You pull up, a robotic arm docks with the car. You don't even have to get out (kind of like the old days of gas jockeys!) Once the connection system is automated, weight and stiffness of the wires don't matter (within reason), and if the system is fully sealed, perhaps higher voltages can be safely considered.

Incidental times - waiting for a human to get out of the car, fiddle around with the connection, later do the opposite to disconnect - go down, too. Since you have an electrical connection to the car, doing the payment processing automatically is straightforward - you just need some appropriate ID chip in the car (akin to a phone SIM card).

The chargers get more expensive, of course. Perhaps we end up with two kinds of chargers: Automated/fast/only at the larger stations/premium charged for use to amortize the cost; manual/slower/spread all over/good for a top-up or charging during time when the car would be stopped anyway. -- Jerry

Again, if it's easy and convenient to charge, then people generally require *less* range. Routinely driving more than 100-150km in a stretch is *relatively* rare. Even folks in sales who might drive 5,000+km per month (~$4k per year in gas at $4/gallon, 30mpg) will often have routes that have lots of stops, for example.

There are still cases where that long distance is necessary. My parents would go to see the grandparents in Chicago from Iowa City. They would drive b/c it's easier and a lot less expensive than buying airline tickets to get there and immediately also renting a car there.

My Mom still goes to visit her sister in Ft. Wayne, IN. She drives there as well. While she has had to gas up on the way, it is only once during the trip there or back.

I don't know about you, but I would like a break after driving 150km.

Don't forget, this battery is flexible. Meaning, the can probably fit more of it in the car, as it can bend to the shape of the vehicle itself. So the range could be extended to say maybe 200-250km. And at those distances, you definitely should be taking a break.

Heck, you'd need one just to go to the loo.

So pull into a service station. A cup of coffee, and loo trip, and there is your 15-20 minutes already. And you're good to go another 200-250km.

It's not so much as a problem as you're making it out to be in my honest opinion.